docs: def currency_context(context):
      """
      Use instead of context processor
      Context variables are only valid within the block scope
      """
      request = context['request']
      currency_code = memoize_nullary(lambda: get_currency_code(request))
  
      context['CURRENCIES'] = Currency.active.all() # querysets are already lazy
      context['CURRENCY_CODE'] = currency_code # lazy
      context['CURRENCY'] = memoize_nullary(lambda: get_currency(currency_code)) # lazy
  
      return ''